Automatic shifting planetary gear power transmissions have a control valve system that includes shift control valves for controlling the interchange of friction devices (clutches and brakes) which establish the power flow paths in planetary gearing.
The valve system includes a valve body in which the control valves are slidably disposed for linear movement in a longitudinal direction. Generally, each shift valve controls the interchange of two friction devices, or in some instances, a single friction device.
If the transmission has five speed ratios, four shift valves are required. This requires the valve body to be sufficiently large to accommodate the four shift valves plus the other required valving. The valve body must also contain the fluid passages ("worm tracks") that interconnect the shift valves with the proper friction devices and with the proper pressure sources.